Vicksburg was a key military point on the eastern side of the Mississippi River, located high on a bluff near the outlet of the Yazoo River. Confederate guns in the heights prevented Union traffic from moving in either direction. In the spring of 1862, the Union position on the Mississippi improved considerably when Captain David G. Farragut and his fleet of 50 ships sailed from the Gulf of Mexico up to New Orleans. He took the city on May 1, leaving it under the control of a Union army commanded by Benjamin F. Butler. This key position remained in Union hands for the remainder of the war. With the mouth of the Mississippi opened, U.S. Grant made Vicksburg a prime target. Efforts were made in May and June of 1862 to attack the city from the river, but to no avail. Later an overland push was made from the north side of the city where Union engineers devised an intricate scheme for draining a swampy area to allow the passage of soldiers. This effort also failed. In the spring of 1863, Grant managed to send Union ships past the Vicksburg defenses in the dead of night. Soldiers that had marched down the west side of the river were then transported across by ship in order to attack the city from the east. In May 1863 a siege was begun, lasting six weeks. Vicksburg fell on July 4, 1863. Several days later Port Hudson, Louisiana, also fell into Union hands, opening the entirety of the Mississippi to Union traffic. The Northern victory at Vicksburg not only split the Confederacy in two, but also freed Grant’s army for action in other theaters.